Ing. Jan Novotný

This study presents a proof of the concept of a deuterium hybrid X-pinch configuration, driven by a 3 kJ dense plasma focus (PFZ-200) at the Czech Technical University in Prague. The system consists of two opposing conical electrodes filled with deuterium gas, forming a point-like source of DD fusion protons via D(d,p)T reactions. Two axial anode-cathode (A–K) gaps of 3 and 5 mm were investigated. Key diagnostics included CR-39-based proton imaging, pinhole camera, and energy spectrometry. The smaller A-K gap (3 mm) produced a compact, nearly circular proton source with a diameter of 1.2 mm and yields on the order of $10^7$ protons/shot. Based on the spectral measurements, the maximum proton energy reached 3.6~MeV, corresponding to deuteron energies approximately up to 1.3 MeV. Compared to standard plasma focus operation, the hybrid X-pinch configuration provided improved proton source localization suitable for advanced plasma diagnostics such as proton imaging and deflectometry.

Ion acceleration in Z-pinch plasmas is traditionally linked to the axial direction of current. Here, we report the radial emission of MeV protons from a low-mass, hydrogen-containing X pinch. Proton energies up to 3 MeV are observed in a hybrid X pinch with a 30 & micro;m polyethylene fiber at a 400 kA peak current. The lowmass load, correlation of protons with hard x-rays, and timing of hard x-ray emission point to proton acceleration driven by current disruption following fiber disintegration. A new insight into the acceleration mechanism arises from the use of an interelectrode gap that is too short for magnetic fields to bend axially accelerated protons by pi /2 radians; thus, the observed radial emission implies a substantial radial acceleration component. The radial emission also enables X-pinch-driven proton radiography, the exceptional potential of which is demonstrated with exploding wires.

Neutron diagnostics is essential for studying fusion reactions and other high-energy neutron sources. This work presents the next generation of the Silver Activation Counter (SAC v3), a detector with a large dynamic range optimized for measuring short bursts of fast neutrons. The SAC v3 utilizes neutron activation of silver isotopes, followed by beta decay detection using Geiger–Müller tubes. We implemented a new electronic design to enable high-speed pulse detection, allowing for accurate measurement of pulses shorter than 100 μs and preventing saturation in measuring high-yield neutron sources. We calibrated the detector experimentally using an AmBe neutron source. For a more accurate determination of neutron yield, we conducted detailed neutron transport simulations using OpenMC. These simulations provided correction coefficients that accounted for differences between the AmBe calibration source and experimental neutron spectra produced by the D(d,n)3He fusion reaction. The SAC v3 achieves a dynamic range from 10^7 to over 10^11 neutrons per shot, making it suitable for high-power laser-driven neutron sources, z-pinch devices, plasma-focus experiments, and tokamaks. The uncertainty of neutron yield measurement remains below 14 % and drops under 10 % with recommended settings. The detector features automated data processing, a web-based control interface, and a cost-effective design, making it an accessible tool for academic and industrial fusion research.

Ultrabright, well-collimated MeV bremsstrahlung radiation was generated through the interaction of high-current electron beams produced via direct laser acceleration (DLA) with a high-𝑍 converter. The DLA mechanism was initiated by a 200 TW, subpicosecond PHELIX laser pulse at a moderately relativistic intensity of (1–2) × 1019 W ⁢cm−2, delivering approximately 60 J of energy into preionized, overcritical-density foam targets. The electron spectrum measured along the laser axis exhibited an effective temperature of approximately 30 MeV and energies exceeding 100 MeV, with a total charge of about 300 nC for electrons with energies >1.5 ⁢MeV (ponderomotive potential), while 100 nC of them is directed along the laser axis within a half-angle cone of 12∘. The directed fraction of DLA electrons with energies exceeding 7.5 MeV carries a charge of 20 to 30 nC, corresponding to a flux up to 2 ×1024 sr−1 s−1. These high-current relativistic electron beams efficiently generate MeV x-rays, enabling the subsequent production of isotopes, positrons, and neutrons with exceptional yield and application potential. In laser shots employing overcritical-density foam targets placed in front of a high-𝑍 converter, bremsstrahlung photons with energies up to 70 MeV were generated and analyzed via nuclear activation of tantalum and gold. The formation of the isotopes 174⁢Ta and 190⁢Au, whose photonuclear cross-section peaks at approximately 65 MeV, confirmed the presence of high-energy photons. In contrast, no activation was observed in control shots where the laser was directed onto the converter without foam, indicating that high-energy photon generation is intrinsically linked to the DLA process in the preionized foam targets. Autoradiographic measurements revealed a divergence of the bremsstrahlung beam of approximately 22∘ (half-angle) in the 14–21-MeV range. These diagnostics indicate an unprecedented photon flux of approximately 2 ×1022 sr−1 s−1, corresponding to about 1011 photons per shot with energies exceeding 7.5 MeV. The conversion efficiency of focused laser energy to bremsstrahlung photons is greater than 1% (within the FWHM of x-ray beam and laser beam). More than 2 ×109 photoneutrons per shot were emitted isotropically, corresponding to a peak flux of 2 ×1020 cm−2 s−1 (4 ×1018 cm−2 s−1 J−1 of laser energy on target). This approach demonstrates a robust and scalable method for generating ultraintense MeV photon beams at kilojoule, petawatt-class laser facilities operating at moderate relativistic intensities, with strong implications for high-energy-density physics and nuclear astrophysics research.

The analysis of Z-pinch implosion dynamics plays one of the most important roles in the study of pulsed power discharges. At the same time, it is difficult to determine the density distribution together with the current density (current coupling to the imploding layer) to provide more detailed information about the dynamics. Numerical simulations can now provide high-resolution results that are almost unattainable in experiments. The challenge, however, is to obtain reliable results that are close enough to the experimental data to describe individual physical phenomena. In this paper, we show that it is possible to use a combination of experimental data and magnetohydrodynamic (MHD) simulations to verify and identify the physical processes during the stagnation of a Z-pinch. We focus on the analysis of the density profile from experimental data of the mega-ampere plasma focus PF-1000 and its reconstruction using an extended MHD code. Thanks to multi-frame interferometry, we recorded a total of 29 interferometric images of two shots, each in a 200 ns time window around the pinch phase. We were then able to obtain density profiles and observe the reflection of the shock wave from the axis. By the appropriate choice of initial conditions and boundary values in the simulation, we were able to obtain reasonable agreement with the experimental values. We also evaluated the possible shortcomings of the 1D simulation, such as mass loss and current flow at the periphery.

This paper presents the filamentary structure of the pinched column in a smaller plasma focus device filled with deuterium. The deflections were observed using schlieren and differential interferometry techniques. The observed filaments have a transverse diameter of 40-200 mu m, which could be interpreted based on the electric current hypothesis as local concentrations of electric current. The evolution of filaments was compared with global structures recorded by extra ultraviolet frames. These results provide a basis for considering the possibility of a filamentary composition of the poloidal current in compact structures. The model of filaments with a helical shape of electrical current may be able to explain the central narrow and dense cord in the axis of the column, the different lifetimes of the structures, and the submillimeter sources of fast electrons and ions.

Direct laser acceleration (DLA) of electrons in plasmas of near-critical density (NCD) is a very advancing platform for high-energy PW-class lasers of moderate relativistic intensity supporting Inertial Confinement Fusion research. Experiments conducted at the PHELIX sub-PW Nd:glass laser demonstrated application-promising characteristics of DLA-based radiation and particle sources, such as ultra-high number, high directionality and high conversion efficiency. In this context, the bright synchrotron-like (betatron) radiation of DLA electrons, which arises from the interaction of a sub-ps PHELIX laser pulse with an intensity of 1019 W/cm2 with pre-ionized low-density polymer foam, was studied. The experimental results show that the betatron radiation produced by DLA electrons in NCD plasma is well directed with a half-angle of 100-200 mrad, yielding (3.4 +/- 0.4)1010 photons/keV/sr at 10 keV photon energy. The experimental photon fluence and the brilliance agree well with the particle-in-cell simulations. These results pave the way for innovative applications of the DLA regime using low-density pre-ionized foams in high energy density research.

We report on the results of point-projection ion deflectometry measurements from a mid-size university z-pinch experiment. A 1 MA 8 kJ LTD generator at the University of Michigan (called MAIZE) drove a hybrid x-pinch (HXP) with a deuterated polyethylene fiber load to produce a point-like source of MeV ions for backlighting. In these experiments, 2.7 MeV protons were generated by DD beam-target fusion reactions. Due to the kinematics of beam-target fusion, the proton energies were down-shifted from the more standard 3.02 MeV proton energy that is released from the center-of-mass rest frame of a DD reaction. In addition to the 2.7 MeV protons, strongly anisotropic beams of 3 MeV accelerated deuterons were detected by ion diagnostics placed at a radial distance of 90 mm from the x-pinch. Numerical reconstruction of experimental data generated by deflected hydrogen ion trajectories evaluated the total current in the vacuum load region. Numerical ion-tracking simulations show that accelerated deuteron beams exited the ion source region at large angles with respect to the pinch current direction.

The neutron and x-ray production is investigated in various pulse-power devices for a deeper understanding of the ion and electron acceleration mechanisms and the application of pulsed neutron sources. We present the extensive results from an anode shape experiment carried out on the PFZ-200 plasma focus device. The various shapes of anodes were tested, including cylinders, tapers, or rounded tips. The experimental shots with a peak current above 200 kA were performed in pure deuterium working gas at 280–600 Pa pressure to obtain maximal neutron yield for each anode shape. The average neutron yields are in the range of (1–2) ×108 neutrons/shot. Outstanding findings about x-ray emission were obtained with the group of tapered anode tips. Using the scintillation detectors shielded by 5 cm thick lead bricks, we obtained the hard x-ray signals with photons exceeding 600 keV energy. Such relatively high x-ray energy indicates the optimized conditions for electron and ion acceleration. At the same time, the individual shots have been well reproducible. Therefore, we were able to study plasma dynamics with the schlieren images taken at different times at different shots.

Filament-like structures were observed during discharges in a small 3-kJ plasma focus device operated with pure deuterium. These structures were recorded by means of two different laser diagnostic techniques: a schlieren system and a differential laser interferometry. They present the novel fine-scale (submillimeter) plasma structures recorded during the radial implosion, at the pinch stagnation, at the development of instabilities, and during a decay of the dense plasma column, when hard x-rays and fusion-produced neutrons were generated. The temporal uncertainty of these observations was about 2 ns, and the spatial one amounted to 40 mu m. The filamentation seems be a natural and spontaneous process which occurs in high-current, hot, and dense plasmas produced in plasma focus devices. The observed filaments have usually longitudinal and/or azimuthal orientations. Their higher plasma density and appearance in regions of the measured and assumed current flows can be interpreted as the formation of plasma-current filaments with concentrated magnetic energy. These filamentary effects should be studied due to their possible role during the evolution of instabilities and the formation of small sources emitting fast electrons and ions.

Fifteen-frames interferometric diagnostics at the PF-1000 facility was enhanced by adding four frames of the schlieren diagnostics and by splitting of four channels in the optical delay line. This setup enabled the visualization of gradients in the plasma density perpendicular to the direction of the diagnostic laser beam, and their relationship with larger structures visualized by using laser interferometry. The schlieren pictures showed filamentary structures of submillimeter 200–300 lm diameter in shots performed with pure deuterium filling. Filaments were observed in a thin (millimeter-thick) lateral-boundary layer, in lobules, and in internal fast transforming regions of the dense plasma column. Their high-density gradients and location in the regions of recorded (or inferred) currents indicated local concentrations of the magnetic field and current distribution. Millimeter- and submillimeter-size sources of fast charged particles, which were identified in the recorded ion pinhole pictures, have been conjectured to be a manifestation of high local concentrations of the magnetic energy.

Dynamics of the implosion of the dense plasma focus play an essential role in converting electrical energy into the kinetic energy of the current sheath and subsequent production of accelerated electrons, ions, hard X-ray, and neutron emission. This paper presents the analysis of the implosion parameters, such as the implosion velocity and imploding mass, coupled with electrical parameters observed on the PF-1000 facility with a modified electrode system. The first two parameters are based on the 16-frame Mach–Zehnder interferometer, which provides the spatial distribution of electron density in a time sequence. Measurement of the total current, current derivative, and voltage enables us to evaluate the total inductance and kinetic energy driven by the capacitor bank. Then comparing the inductances and kinetic energies evaluated from the interferograms and electrical waveforms can provide more precise information on the current flowing in the imploding sheath. We present a possible way to deal with the fact that only part of the total current flows through the imploding layer. With the supposition that the rest of the current flows close to the insulator, we conclude that roughly 70% of the total current flows through the pinch, which is in good agreement with an input parameter of the Lee model, for example.

This paper concerns the correlation of hard x-ray and neutron signals, which were recorded with scintillation detectors oriented in the axial and radial directions, in a comparison with interferometric and extreme-ultraviolet radiation frames, as recorded within the plasma focus (PF)-1000 facility operated with a deuterium filling. The considered signals showed two different phases. In the initial phase, the fusion neutrons are mainly produced by deuterons moving dominantly downstream during the disruption of a pinch constriction (lasting tens nanoseconds). In the later phase (usually after about 100 ns), the fusion neutron emission reaches its maximum in the radial directions. This emission (lasting 100–200 ns) is caused by the fast deuterons moving in both the downstream and radial directions. It correlates usually with a decay of dense plasma structures in remnants of the expanding pinch column. This can be explained by a decay of internal magnetic fields. The neutron signal is usually composed of several sub-pulses of different energies. It was deduced that the primary deuterons producing the observed fusion neutrons undergo a regular and repeated temporal, directional, and energy evolution.

Z-pinches have been explored as efficient soft x-ray sources for many years. To optimize x-ray emission, various z-pinch configurations were tested. This paper presents data obtained with a hybrid gas-puff z-pinch imploding onto on-axis wires on a microsecond, multi-megaampere GIT-12 generator. In our previous experiments, the hybrid gas puff, i.e., an inner deuterium gas puff surrounded by an outer hollow cylindrical plasma shell, was used to produce energetic protons, deuterons, and neutrons up to 60MeV [Klir et al., New J. Phys. 22, 103036 (2020)]. The behavior of the hybrid gas-puff z-pinch on GIT-12 was interpreted as a high-density plasma opening switch with a microsecond conduction time, 3 MA conduction current, nanosecond opening, and up to 60MV stand-off voltage. These properties can be employed to transfer the current into an on-axis load with a high rise rate. In the recent experiments on GIT-12, we therefore placed single or multiple aluminum wires on the axis of the hybrid gas-puff z-pinch. Before a current sheath arrived at the axis, a coronal plasma was seen around the wire. A rapid increase in x-ray radiation was observed when the coronal plasma imploded onto the axis. The coronal plasma implosion resulted in a long (2cm), narrow (similar to mm) column radiating in the Al K-shell lines. With the single Al wire of 80 mu m diameter, the K-shell x-ray output reached 5.5 +/- 0.8kJ in a 0.6 +/- 0.1 TW peak power and 7 +/- 1ns pulse. The higher K-shell yield of 12 +/- 2kJ and peak K-shell power of 0.7 +/- 0.1 TW were achieved with four 38 mu m diameter Al wires. (Their cross section formed the corners of a square with 1mm side.) The presence of the wires on the axis significantly suppressed ion acceleration and neutron production. Deuterium-deuterium (DD) neutron yields of about 1.2x10(11) were 20 times smaller than the yields produced in shots without any wire. The DD neutron yield was increased up to 4.5x10(11) when the Al wire was replaced by a fiber fr

B-field measurements are crucial for the study of high-temperature and high-energy-density plasmas. A successful diagnostic method, ion deflectometry (radiography), is commonly employed to measure MGauss magnetic fields in laser-produced plasmas. It is based on the detection of multi-MeV ions, which are deflected in B-fields and measure their path integral. Until now, protons accelerated via laser–target interactions from a point-like source have been utilized for the study of Z-pinch plasmas. In this paper, we present the results of the first Z-pinch-driven ion deflectometry experiments using MeV deuterium beams accelerated within a hybrid gas-puff Z-pinch plasma on the GIT-12 pulse power generator. In our experimental setup, an inserted fiducial deflectometry grid (D-grid) separates the imploding plasma into two regions of the deuteron source and the studied azimuthal B-fields. The D-grid is backlighted by accelerated ions, and its shadow imprinted into the deuteron beams demonstrates ion deflections. In contrast to the employment of the conventional point-like ion source, in our configuration, the ions are emitted from the extensive and divergent source inside the Z-pinch. Instead of having the point ion source, deflected ions are selected via a point projection by a pinhole camera before their detection. Radial distribution of path-integrated B-fields near the axis (within a 15 mm radius) is obtained by analysis of experimental images (deflectograms). Moreover, we present a 2D topological map of local azimuthal B-fields B(r,z) via numerical retrieval of the experimental deflectogram.

This article presents a study of neutron emission on the PFZ-200 plasma focus at the Department of physics on FEE CTU in Prague, Czech Republic. In order to achieve the highest and most stable neutron yields, the deuterium working gas pressure and the anode shape were systematically varied. We observed the plasma time to the pinch and the discharge current by the Rogowski coil and neutron emission by the silver activation detector and scintillation time-of-flight detectors. The imploded plasma was visualized using a fast X-ray pinhole camera with a gated microchannel plate detector. The experiment presents the z-pinch discharges with the current maximum above 200 kA and the average neutron yields of 3×10^8 neutrons/shot. Measured pinch times were in the range from 1.65 to 1.85 μs . The hollow round anode configuration performed the most stable neutron yields with a deviation under 20%.

Deuterium gas-puff z-pinches are very efficient laboratory sources of neutron pulses. Using a novel hybrid gas-puff load on the GIT-12 generator, a significant increase in the neutron yields up to